WASHINGTON - Senate passage of a historic restructuring of the nation's health-insurance system appeared more certain yesterday as key lawmakers praised, and President Obama endorsed, a tentative deal to get the stalled bill moving.

Obama said he supported the proposal that Senate Democratic negotiators crafted Tuesday night, "especially since it's aimed at increasing choice and competition and lowering cost."

Few details were released, but the deal appeared to solve a problem that has stymied progress: a split over creating a government-run health-care plan, or public option.

Under the compromise, such a plan would be a backup, used only if insurers failed to meet certain standards. Instead, Medicare would expand and a federal agency would oversee a new national, privately run insurance system.

Sen. Joe Lieberman (I., Conn.), who had threatened to try to kill any plan that had a public option, said he was encouraged by the latest news.

Sens. Mary Landrieu (D., La.) and Blanche Lincoln (D., Ark.), also potential swing votes, expressed sympathy for aspects of the compromise while stopping short of endorsing it, pending a cost assessment by the Congressional Budget Office, or CBO.

But "the ball's moving forward," said John Fortier, a research fellow at Washington's American Enterprise Institute, a right-leaning research group.

The fate of the deal rests with the nonpartisan CBO, which is to report on its potential cost in a few days.

"We certainly will await that, as well," White House press secretary Robert Gibbs said, indicating that even administration officials weren't sure precisely what the compromise would look like.

This much was apparent: A new government-run plan to compete with private insurers, long sought by liberals and the White House, was barely alive.

Instead, the federal Office of Personnel Management, the agency that runs the Federal Employees Health Benefits Program, would oversee national insurance plans.

And Medicare, the government insurer of people older than 65 and some others with disabilities, would be expanded so that certain 55- to 64-year-olds could sign on for coverage.

The benefit of national plans, proponents said, is that they would have greater leverage with providers in setting payment rates.

But some were skeptical that oversight by the Office of Personnel Management would bring better rates, noting that insurance premiums for the federal plans, which serve 11 million U.S. employees, including members of Congress, increased by nearly 9 percent this year.

As Gibbs described the White House's general understanding of the Senate's vision, U.S. consumers could purchase the private plans through the federally managed menu, akin to how federal employees choose their insurance coverage.

Landrieu said the 10 moderates and liberals who had engaged in days of private talks on a compromise believed the new Medicare plan was "a good idea."

Lincoln said the government-supervised insurance idea "takes the best of both worlds. The government creates an environment where private industry can operate, but creates an environment in a way where the private industry is creating a product that meets the needs of the consumer."

At the same time, Lincoln cautioned, "there are a lot of things on the table, still."

Obama praised the Senate for making "critical progress last night with a creative new framework that I believe will help pave the way for final passage and a historic achievement on behalf of the American people."

Opponents on both ends of the spectrum pushed back.

"If the health-care bill doesn't include a public option, it'll be a huge giveaway to the insurance companies," the liberal MoveOn.org said in an e-mail to its members.

Rick Scott of Conservatives for Patients' Rights called the deal an "OPM plan," or "government-run health care with other people's money."

The bill passed by the House includes a public option. If the Senate goes ahead without one, the difference would need to be reconciled before any health overhaul could be sent to Obama to become law.

Insurance and medical interests had concerns about Medicare expansion.

"Any Medicare buy-in would invariably lead to [crowding] out of the private health-insurance market," the Federation of American Hospitals warned.

American Medical Association president J. James Rohack, a physician, reiterated the group's long-standing opposition to expanding Medicare, "given the fiscal projections for the future."

The key to passing anything in the Senate rests with a handful of Democratic moderates. The party controls 60 of the 100 Senate seats, and 60 votes are needed to cut off debate, so any defection could doom the bill.

The latest plan offered the leaders hope that moderates would go along, and that perhaps they would be able to win over two Republican centrists, Sens. Olympia Snowe and Susan Collins of Maine.

Leaders are hoping for a final vote on the 10-year plan, currently estimated to cost $848 billion, by Christmas.

This article includes information from the Washington Post.